Everyone only on the Bulgarian server and only in vanilla1 has very high ping all the time, regardless of their location, when anyone goes to another room, the ping goes back to normal for them

How many mice were there?

Somewhere around 20

It may be because of that,not sure though

This looks like satellite servers' issue. Players in the rooms that are created on a server with a lot of lag, get much higher ping.
If you should face it when you create a room, just leave and re-create another room.